1. Field of the Invention
The present invention relates to a taking optical system and an image sensing apparatus, and particularly to a taking optical system that offers a variable image sensing magnification and a high zoom ratio.
2. Description of Related Art
As personal computers become widespread, digital cameras, which permit easy acquisition of images, have been becoming widespread in recent years. It is nowadays common to incorporate a digital camera into a data processing device such as a mobile computer, a cellular phone, or a personal digital assistant (PDA). Under these circumstances, increasingly compact digital still cameras are sought after, resulting in demands for further down-sizing of taking optical systems.
On the other hand, in image sensors that are used to convert light into an electrical signal, various advancements have been made for higher and higher performance in terms of, for example, the number of pixels they have, creating a shortening tendency of the product cycles of digital cameras. Thus, taking optical systems are now required not only to be compact but also to offer high performance and be easy to manufacture.
Digital cameras typically employ, as their taking optical systems, zoom optical systems. Such zoom optical systems are conventionally designed to offer a zoom ratio of typically 2 to 5, but are now required to offer twice as high a zoom ratio. In fact, there have conventionally been known some zoom optical systems that meet this requirement. Japanese Laid-open Patent Publication No. H09-90221, for example, discloses a zoom optical system that offers a zoom ratio of 15 or more.
Although such conventional zoom optical systems offer high zoom ratios, they are not satisfactorily compact, nor do they offer satisfactorily high performance. The zoom optical system disclosed in the above-mentioned publication, for example, has an unduly large total length at the wide-angle end, and suffers from unsatisfactorily corrected aberrations.